There is a related module called Net::SSLeay::Handle included in this distribution that you might want to use instead. It has its own pod documentation.

This module offers some high level convinience functions for accessing web pages on SSL servers (for symmetry, same API is offered for accessing http servers, too), a sslcat() function for writing your own clients, and finally access to the SSL api of SSLeay/OpenSSL package so you can write servers or clients for more complicated applications.

For high level functions it is most convinient to import them to your main namespace as indicated in the synopsis.

Case 1 demonstrates typical invocation of get_https() to fetch an HTML page from secure server. The first argument provides host name or ip in dotted decimal notation of the remote server to contact. Second argument is the TCP port at the remote end (your own port is picked arbitrarily from high numbered ports as usual for TCP). The third argument is the URL of the page without the host name part. If in doubt consult HTTP specifications at <http://www.w3c.org>

Case 2 demonstrates full fledged use of get_https(). As can be seen, get_https() parses the response and response headers and returns them as a list, which can be captured in a hash for later reference. Also a fourth argument to get_https() is used to insert some additional headers in the request. make_headers() is a function that will convert a list or hash to such headers. By default get_https() supplies Host (make virtual hosting easy) and Accept (reportedly needed by IIS) headers.

Case 2b demonstrates how to get password protected page. Refer to HTTP protocol specifications for further details (e.g. RFC2617).

Case 3 invokes post_https() to submit a HTML/CGI form to secure server. First four arguments are equal to get_https() (note that empty string ('') is passed as header argument). The fifth argument is the contents of the form formatted according to CGI specification. In this case the helper function make_https() is used to do the formatting, but you could pass any string. The post_https() automatically adds Content-Type and Content-Length headers to the request.

Case 4 shows the fundamental sslcat() function (inspired in spirit by netcat utility :-). Its your swiss army knife that allows you to easily contact servers, send some data, and then get the response. You are responsible for formatting the data and parsing the response - sslcat() is just a transport.

Case 5 is a full invocation of sslcat() which allows return of errors as well as the server (peer) certificate.

The $trace global variable can be used to control the verbosity of high level functions. Level 0 guarantees silence, level 1 (the default) only emits error messages.

The above mentioned functions actually return the response headers as a list, which only gets converted to hash upon assignment (this assignment looses information if the same header occurs twice, as may be the case with cookies). There are also other variants of the functions that return unprocessed headers and that return a reference to a hash.

All of the above code fragments accomplish the same thing: display all values of all headers. The API functions ending in "3" return the headers simply as a scalar string and it is up to the application to split them up. The functions ending in "4" return a reference to hash of arrays (see perlref and perllol manual pages if you are not familiar with complex perl data structures). To access single value of such header hash you would do something like

print $headers_ref{COOKIE}[0];

The variants 3 and 4 also allow you to discover the server certificate in case you would like to store or display it, e.g.

Beware that this method only allows after the fact verification of the certificate: by the time get_https3() has returned the https request has already been sent to the server, whether you decide to tryst it or not. To do the verification correctly you must either employ the OpenSSL certificate verification framework or use the lower level API to first connect and verify the certificate and only then send the http data. See implementation of ds_https3() for guidance on how to do this.

Secure web communications are encrypted using symmetric crypto keys exchanged using encryption based on the certificate of the server. Therefore in all SSL connections the server must have a certificate. This serves both to authenticate the server to the clients and to perform the key exchange.

Sometimes it is necessary to authenticate the client as well. Two options are available: http basic authentication and client side certificate. The basic authentication over https is actually quite safe because https guarantees that the password will not travel in clear. Never-the-less, problems like easily guessable passwords remain. The client certificate method involves authentication of the client at SSL level using a certificate. For this to work, both the client and the server will have certificates (which typically are different) and private keys.

The API functions outlined above accept additional arguments that allow one to supply the client side certificate and key files. The format of these files is the same as used for server certificates and the caveat about encrypting private key applies.

OpenSSL supports the ability to verify peer certificates. It can also optionally check the peer certificate against a Certificate Revocation List (CRL) from the certificates issuer. A CRL is a file, created by the certificate issuer that lists all the certificates that it previously signed, but which it now revokes. CRLs are in PEM format.

After setting this flag, if OpenSSL checks a peer's certificate, then it will attempt to find a CRL for the issuer. It does this by looking for a specially named file in the search directory specified by CTX_load_verify_locations. CRL files are named with the hash of the issuer's subject name, followed by .r0, .r1 etc. For example ab1331b2.r0, ab1331b2.r1. It will read all the .r files for the issuer, and then check for a revocation of the peer cerificate in all of them. (You can also force it to look in a specific named CRL file., see below). You can find out the hash of the issuer subject name in a CRL with

openssl crl -in crl.pem -hash -noout

If the peer certificate does not pass the revocation list, or if no CRL is found, then the handshaking fails with an error.

You can also force OpenSSL to look for CRLs in one or more arbitrarily named files.

randomize() seeds the eay PRNG with /dev/urandom (see top of SSLeay.pm for how to change or configure this) and optionally with user provided data. It is very important to properly seed your random numbers, so do not forget to call this. The high level API functions automatically call randomize() so it is not needed with them. See also caveats.

set_cert_and_key() takes two file names as arguments and sets the certificate and private key to those. This can be used to set either cerver certificates or client certificates.

dump_peer_certificate() allows you to get plaintext description of the certificate the peer (usually server) presented to us.

ssl_read_all() and ssl_write_all() provide true blocking semantics for these operations (see limitation, below, for explanation). These are much preferred to the low level API equivalents (which implement BSD blocking semantics). The message argument to ssl_write_all() can be reference. This is helpful to avoid unnecessary copy when writing something big, e.g:

ssl_read_CRLF() uses ssl_read_all() to read in a line terminated with a carriage return followed by a linefeed (CRLF). The CRLF is included in the returned scalar.

ssl_read_until() uses ssl_read_all() to read from the SSL input stream until it encounters a programmer specified delimiter. If the delimiter is undefined, $/ is used. If $/ is undefined, \n is used. One can optionally set a maximum length of bytes to read from the SSL input stream.

In addition to the high level functions outlined above, this module contains straight forward access to SSL part of OpenSSL C api. Only the SSL subpart of OpenSSL is implemented (if anyone wants to implement other parts, feel free to submit patches).

See ssl.h header from OpenSSL C distribution for list of low lever SSLeay functions to call (to check if some function has been implemented see directly in SSLeay.xs). The module strips SSLeay names of the initial "SSL_", generally you should use Net::SSLeay:: in place. For example:

You can also use Net::SSLeay::print_errs() to dump the error stack without exiting the program. As can be seen, your code becomes much more readable if you import the error reporting functions to your main name space.

I can not emphasize enough the need to check error returns. Use these functions even in most simple programs, they will reduce debugging time greatly. Do not ask questions in mailing list without having first sprinkled these in your code.

Perl uses file handles for all I/O. While SSLeay has quite flexible BIO mechanism and perl has evolved PerlIO mechanism, this module still sticks to using file descriptors. Thus to attach SSLeay to socket you should use fileno() to extract the underlying file descriptor:

Net::SSLeay::set_fd($ssl, fileno(S)); # Must use fileno

You should also use "$|=1;" to eliminate STDIO buffering so you do not get confused if you use perl I/O functions to manipulate your socket handle.

If you need to select(2) on the socket, go right ahead, but be warned that OpenSSL does some internal buffering so SSL_read does not always return data even if socket selected for reading (just keep on selecting and trying to read). Net::SSLeay.pm is no different from the C language OpenSSL in this respect.

At this moment the implementation of verify_callback is crippeled in the sense that at any given time there can be only one call back which is shared by all SSL contexts, sessions and connections. This is due to having to keep the reference to the perl call back in a static variable so that the callback C glue can find it. To remove this restriction would require either a more complex data structure (like a hash?) in XSUB to map the call backs to their owners or, cleaner, adding a context pointer in the SSL structure. This context would then be passed to the C callback, which in our case would be the glue to look up the proper Perl function from the context and call it.

Callbacks for decrypting private keys are implemented, but have the same limitation as the verify_callback implementation (one password callback shared between all contexts.) You might use it something like this:

Over the years it has become clear that it would be convenient to use the light weight flavour API of Net::SSLeay also for normal http (see LWP for heavy weight object oriented approach). In fact it would be nice to be able to flip https on and off on the fly. Thus regular http support was evolved.

Yet another echo server. This one runs from /etc/inetd.conf so it avoids all the socket code overhead. Only caveat is opening rsa key file - it had better be without any encryption or else it will not know where to ask for the password. Note how STDIN and STDOUT are wired to SSL.

There are also a number of example/test programs in the examples directory:

sslecho.pl - A simple server, not unlike the one above
minicli.pl - Implements a client using low level SSLeay routines
sslcat.pl - Demonstrates using high level sslcat utility function
get_page.pl - Is a utility for getting html pages from secure servers
callback.pl - Demonstrates certificate verification and callback usage
stdio_bulk.pl - Does SSL over Unix pipes
ssl-inetd-serv.pl - SSL server that can be invoked from inetd.conf
httpd-proxy-snif.pl - Utility that allows you to see how a browser
sends https request to given server and what reply
it gets back (very educative :-)
makecert.pl - Creates a self signed cert (does not use this module)

Net::SSLeay::read uses internal buffer of 32KB, thus no single read will return more. In practice one read returns much less, usually as much as fits in one network packet. To work around this, you should use a loop like this:

warning if die_if_ssl_error is made autoloadable. If you figure out why, drop me a line.

Callback set using SSL_set_verify() does not appear to work. This may well be eay problem (e.g. see ssl/ssl_lib.c line 1029). Try using SSL_CTX_set_verify() instead and do not be surprised if even this stops working in future versions.

Random numbers are not initialized randomly enough, especially if you do not have /dev/random and/or /dev/urandom (such as in Solaris platforms - but I've been suggested that cryptorand daemon from SUNski package solves this). In this case you should investigate third party software that can emulate these devices, e.g. by way of a named pipe to some program.

Another gotcha with random number initialization is randomness depletion. This phenomenon, which has been extensively discussed in OpenSSL, Apache-SSL, and Apache-mod_ssl forums, can cause your script to block if you use /dev/random or to operate insecurely if you use /dev/urandom. What happens is that when too much randomness is drawn from the operating system's randomness pool then randomness can temporarily be unavailable. /dev/random solves this problem by waiting until enough randomness can be gathered - and this can take a long time since blocking reduces activity in the machine and less activity provides less random events: a vicious circle. /dev/urandom solves this dilemma more pragmatically by simply returning predictable "random" numbers. Some /dev/urandom emulation software however actually seems to implement /dev/random semantics. Caveat emptor.

I've been pointed to two such daemons by Mik Firestone <mik@@speed.stdio._com> who has used them on Solaris 8

to cope with some well know bugs in some other SSL implementations. The high level API functions always set all known compatibility options.

Sometimes sslcat (and the high level https functions that build on it) is too fast in signaling the EOF to legacy https servers. This causes the server to return empty page. To work around this problem you can set global variable

$Net::SSLeay::slowly = 1; # Add sleep so broken servers can keep up

http/1.1 is not supported. Specifically this module does not know to issue or serve multiple http requests per connection. This is a serious short coming, but using SSL session cache on your server helps to alleviate the CPU load somewhat.

As of version 1.09 many newer OpenSSL auxiliary functions were added (from REM_AUTOMATICALLY_GENERATED_1_09 onwards in SSLeay.xs). Unfortunately I have not had any opportunity to test these. Some of them are trivial enough that I believe they "just work", but others have rather complex interfaces with function pointers and all. In these cases you should proceed wit great caution.

This module defaults to using OpenSSL automatic protocol negotiation code for automatically detecting the version of the SSL protocol that the other end talks. With most web servers this works just fine, but once in a while I get complaints from people that the module does not work with some web servers. Usually this can be solved by explicitly setting the protocol version, e.g.

Although the autonegotiation is nice to have, the SSL standards do not formally specify any such mechanism. Most of the world has accepted the SSLeay/OpenSSL way of doing it as the de facto standard. But for the few that think differently, you have to explicitly speak the correct version. This is not really a bug, but rather a deficiency in the standards. If a site refuses to respond or sends back some nonsensical error codes (at SSL handshake level), try this option before mailing me.

The high level API returns the certificate of the peer, thus allowing one to check what certificate was supplied. However, you will only be able to check the certificate after the fact, i.e. you already sent your form data by the time you find out that you did not trust them, oops.

So, while being able to know the certificate after the fact is surely useful, the security minded would still choose to do the connection and certificate verification first and only after that exchange data with the site. Currently none of the high level API functions do this, thus you would have to program it using the low level API. A good place to start is to see how Net::SSLeay::http_cat() function is implemented.

The high level API functions use a global file handle SSLCAT_S internally. This really should not be a problem because there is no way to interleave the high level API functions, unless you use threads (but threads are not very well supported in perl anyway (as of version 5.6.1). However, you may run into problems if you call undocumented internal functions in an interleaved fashion.

"Random number generator not seeded!!!" This warning indicates that randomize() was not able to read /dev/random or /dev/urandom, possibly because your system does not have them or they are differently named. You can still use SSL, but the encryption will not be as strong.

"open_tcp_connection: failed `server', 123 ($!)" The name was resolved, but establising the TCP connection failed.

"msg 123: 1 - error:140770F8:SSL routines:SSL23_GET_SERVER_HELLO:unknown proto" SSLeay error string. First (123) number is PID, second number (1) indicates the position of the error message in SSLeay error stack. You often see a pile of these messages as errors cascade.

"msg 123: 1 - error:02001002::lib(2) :func(1) :reason(2)" The same as above, but you didn't call load_error_strings() so SSLeay couldn't verbosely explain the error. You can still find out what it means with this command:

/usr/local/ssl/bin/ssleay errstr 02001002

Password is being asked for private key This is normal behaviour if your private key is encrypted. Either you have to supply the password or you have to use unencrypted private key. Scan OpenSSL.org for the FAQ that explains how to do this (or just study examples/makecert.pl which is used during `make test' to do just that).

There are currently two perl modules for using OpenSSL C library: Net::SSLeay (maintaned by me) and SSLeay (maintained by OpenSSL team). This module is the Net::SSLeay variant.

At the time of making this release, Eric's module was still quite sketchy and could not be used for real work, thus I felt motivated to make this maintenance release. This module is not planned to evolve to contain any further functionality, i.e. I will concentrate on just making a simple SSL connection over TCP socket. Presumably Eric's own module will offer full SSLeay API one day.

This module uses OpenSSL-0.9.6c. It does not work with any earlier version and there is no guarantee that it will work with later versions either, though as long as C API does not change, it should. This module requires perl5.005, or 5.6.0 (or better?) though I believe it would build with any perl5.002 or newer.

Distribution and use of this module is under the same terms as the OpenSSL package itself (i.e. free, but mandatory attribution; NO WARRANTY). Please consult LICENSE file in the root of the OpenSSL distribution.

While the source distribution of this perl module does not contain Eric's or OpenSSL's code, if you use this module you will use OpenSSL library. Please give Eric and OpenSSL team credit (as required by their licenses).

And remember, you, and nobody else but you, are responsible for auditing this module and OpenSSL library for security problems, backdoors, and general suitability for your application.